1. Field of the Invention
This invention relates to a recordable optical disc such as a DVD-R (a digital versatile disc recordable) or a DVD-RW (a digital versatile disc rewritable). In addition, this invention relates to a method and an apparatus for recording a signal on an optical disc. Furthermore, this invention relates to a recording method and a recording apparatus designed so that a desired level of the recording power of a light beam scanning an optical disc is decided during test recording and reproduction, and then the light beam power is controlled at the desired level during main-data recording which follows the test recording and reproduction.
2. Description of the Related Art
There are recordable optical discs designed to be scanned by a light beam at a constant linear velocity (CLV). Typical examples of such recordable optical discs are a CD-R (a compact disc recordable) and a CD-RW (a compact disc rewritable). It is known that a recordable optical disc is driven while being scanned by a light beam at a linear velocity higher than the standard value.
In the case of CLV-based drive of an optical disc, the rotational speed of the optical disc is increased as a portion of the optical disc which is currently scanned by a light beam radially moves from the outermost position of the optical disc to the innermost position thereof.
As disclosed in Japanese patent application publication number P2001-331940A, in the case of CLV-based drive of an optical disc at a 16-fold linear velocity which means a linear velocity equal to 16 times the standard value, the rotational speed of the optical disc is increased to 8,000 rpm or above when the innermost position of the optical disc is scanned by a light beam. Spontaneous vibration of an optical disc is greater as the rotational speed thereof is higher. Spontaneous vibration of an optical disc is pronounced if the center of gravity of the optical disc is geometrically off-centered.
Generally, a recordable optical disc has a power calibration area (PCA) in addition to a data recording area. The power calibration area is also referred to as the test recording area. The power calibration area is located in the innermost portion of the optical disc. The data recording area extends outward of the power calibration area.
A conventional CLV drive apparatus for a recordable optical disc is designed to subject a light beam to optimum power control (OPC). The conventional drive apparatus implements test recording and reproduction before main-data recording. During the test recording and reproduction, the conventional drive apparatus records a test signal on the power calibration area of the optical disc and reproduces the test signal therefrom while applying the light beam to the power calibration area. The conventional drive apparatus evaluates the reproduced test signal, and decides a desired level (an optimum level) of the recording power of the light beam on the basis of the evaluation result. During the main-data recording, the conventional drive apparatus carries out the recording of main data on the data recording area of the optical disc while controlling the recording power of the light beam at the desired level (the optimum level). In this way, the OPC is carried out. Since the power calibration area is located in the innermost portion of the optical disc, the rotational speed of the optical disc is relatively high during the test recording and reproduction. In the case of high CLV drive, the rotational speed of the optical disc is very high during the test recording and reproduction. The very-high-speed rotation of the optical disc causes considerably great spontaneous vibration thereof which makes unstable the recording and reproduction of the test signal. As a result of the unstable recording and reproduction of the test signal, the decided level of the desired recording power (the optimum recording power) of the light beam is inaccurate so that the OPC is unreliable. In the case of high CLV drive, when an inner portion of the data recording area of the optical disc is scanned by the light beam during the main-data recording, the rotational speed of the optical disc is relatively high and hence great spontaneous vibration of the optical disc occurs. The great spontaneous vibration of the optical disc causes the formation of pits in the optical disc to be unstable.
An on-the-fly writing procedure is designed so that image data is written into a CD-R from a CD-ROM (a compact disc read only memory) without making an image file in a hard disc. According to a known way of implementing the on-the-fly writing procedure at a high speed, image data is reproduced from a CD-ROM while the CD-ROM is scanned by a light beam at a high constant angular velocity (a high CAV), and the reproduced image data is recorded on a CD-R while the CD-R is scanned by a light beam at a high CLV. In this case, when the outermost portion of the data recording area of the CD-ROM is scanned by the light beam, the linear velocity of the CD-ROM relative to the related light beam is equal to about a 32-fold value. On the other hand, when the innermost portion of the data recording area of the CD-ROM is scanned by the light beam, the linear velocity of the CD-ROM relative to the related light beam is equal to about a 16-fold value. Thus, when the innermost portion of the data recording area of the CD-ROM is scanned by the light beam, the image data is reproduced therefrom at an insufficient rate so that buffer under-run tends to occur and hence the writing of the image data into the CD-R tends to be unsuccessful.
Japanese patent application P2001-331940A discloses that during the recording of a signal on a CD-R (or a CD-RW), an inner part of the CD-R is scanned by a light beam on a CAV basis while an outer part thereof is scanned by the light beam on a CLV basis. For example, the CAV recording of the signal on the CD-R is started from the innermost position of a program recording area (a data recording area) in the CD-R under conditions where the linear velocity of the innermost position of the program recording area relative to the light beam is equal to a 12-fold value. When the linear velocity of the currently scanned portion of the CD-R relative to the light beam reaches a 16-fold value, the CAV recording is replaced by the CLV recording. Then, the CLV recording which corresponds to a 16-fold linear velocity is continued. The change between the CAV recording and the CLV recording reduces the maximum rotational speed of the CD-R, and hence suppresses spontaneous vibration of the CD-R. In the case of an on-the-fly writing procedure, the suppression of the spontaneous vibration of the CD-R prevents the writing of the signal into the CD-R from being unsuccessful.
A drive apparatus for the CD-R which can implement the above-mentioned change between the CAV recording and the CLV recording is explained below. During the CAV recording, the linear velocity of the currently scanned portion of the CD-R relative to the light beam varies in time domain, and the optimum recording power of the light beam varies accordingly. Thus, the drive apparatus carries out test recording and reproduction to decide desired recording powers of the light beam for the initial linear velocity (the minimum linear velocity) and the final linear velocity (the maximum linear velocity) regarding the CAV recording. During the CAV recording which follows the test recording and reproduction, a desired recording power of the light beam is decided on the basis of the linear velocity of the currently scanned portion of the CD-R relative to the light beam through interpolation responsive to the desired recording powers of the light beam for the initial linear velocity and the final linear velocity, and the actual recording power of the light beam is controlled at the desired one. During the CLV recording which follows the CAV recording, the actual recording power of the light beam is controlled at the desired recording power for the final linear velocity. The test recording and reproduction use a power calibration area (PCA) located at the innermost position of the CD-R. Since the power calibration area is located at the innermost position of the CD-R, the CD-R is rotated at a very high speed during a stage of the test recording and reproduction which decides a desired recording power of the light beam for the final linear velocity regarding the CAV recording. The very-high-speed rotation of the CD-R causes problems similar to the previously-mentioned ones.
Japanese patent application P2001-331940A discloses a PCA-inner/outer optical disc having a program recording area, an inner power calibration area (an inner test recording area) which extends inward of the program recording area, and an outer power calibration area (an outer test recording area) which extends outward of the program recording area. Japanese patent application P2001-331940A also discloses an optical-disc recorder for a PCA-inner/outer optical disc. The optical-disc recorder in Japanese patent application P2001-331940A implements CAV-based drive of the optical disc when an inner part of the program recording area is scanned by a light beam, and implements CLV-based drive of the optical disc when an outer part of the program recording area is scanned by the light beam. The optical-disc recorder can also implement test recording and reproduction using the inner and outer power calibration areas of the optical disc. Japanese patent application P2001-331940A discloses that examples of the PCA-inner/outer optical disc are a CD-R, a CD-RW, and a DVD-R.
In the PCA-inner/outer optical disc of Japanese patent application P2001-331940A, each of the inner and outer power calibration areas has a test area and a count area. During test recording and reproduction, each time the test area is subjected to OPC test recording (that is, each time the test area is loaded with a test signal), an EFM signal having a quantity of one sub-code frame is recorded on the count area. The EFM signals recorded on the count area represent the boundary between a used portion and a usable portion in the test area. Before new OPC is carried out, a detection is given of the position up to which EFM signals have already been recorded in the count area. Then, on the basis of the detected position, a decision is made as to the position from which test recording in the new OPC should be started in the test area.
In the case of drive of a DVD-R at a constant linear velocity higher than the standard value, a required rotational speed of the DVD-R is excessively high when an innermost portion of the DVD-R is scanned by a light beam. Accordingly, it is basically undesirable to implement test recording and reproduction using the inner power calibration area of the DVD-R. Thus, in this case, it is desirable to carry out only test recording and reproduction using the outer power calibration.
There is a DVD-R which can be driven at a constant linear velocity changeable among a 1-fold value (the standard value), a 2-fold value, a 4-fold value, a 6-fold value, and an 8-fold value. An 8-fold-speed optical-disc recorder drives such a DVD-R at the 8-fold value. In this case, a required rotation speed of the DVD-R is excessively high when an innermost portion of the DVD-R is scanned by a light beam. Accordingly, it is undesirable to implement test recording and reproduction using the inner power calibration area of the DVD-R. Thus, in this case, it is desirable to carry out only test recording and reproduction using the outer power calibration area of the DVD-R. On the other hand, a 2-fold-speed optical-disc recorder drives the DVD-R at the 2-fold value. In this case, a required rotation speed of the DVD-R remains acceptable even when an innermost portion of the DVD-R is scanned by a light beam. Thus, in this case, it is acceptable to carry out test recording and reproduction using both the inner and outer power calibration areas of the DVD-R. As understood from the above explanation, the speed performance of an optical-disc recorder decides whether or not the inner power calibration area of the DVD-R should be used for test recording and reproduction.
The sizes of the inner and outer power calibration areas of a DVD-R are finite. Therefore, under some recording conditions, one of the inner and outer power calibration areas has been fully used for test recording and reproduction, and can not be used any more. Especially, in the case of high-speed drive of a DVD-R, the strategy (the recording light waveform) is complicated and the margin for jitter is small so that a wide area is used for test recording and reproduction. Thus, in this case, one of the inner and outer power calibration areas of the DVD-R has been fully used for test recording and reproduction, and only the other can be used for further test recording and reproduction.
Generally, it is difficult to equalize the recording characteristics of the inner and outer power calibration areas of a DVD-R. In the case where an organic dye film is formed by spin coat during the fabrication of a DVD-R, a recording film in the outer power calibration area is thicker than that in the inner power calibration area. In the case where a resin layer of a polycarbonate substrate for a DVD-R is formed by injection molding from an inner side gate, it is difficult to make uniform the birefringence characteristics throughout a disc surface. Surface vibration and tilt in the outer power calibration area of a DVD-R are greater than those in the inner power calibration area thereof. The outer power calibration area of a DVD-R tends to scratch and be given fingerprints. Therefore, the physical characteristics of the inner power calibration area of a DVD-R differ from those of the outer power calibration area thereof. Thus, it is difficult to obtain exactly equal results of test recording and reproduction using the inner power calibration area of a DVD-R and test recording and reproduction using the outer power calibration area thereof.
There is an 8-fold-speed optical-disc recorder which can operate at either an 8-fold speed or a 4-fold speed during the drive of an optical disc. When surface vibration of the optical disc is great so that control of a spindle motor is unstable or when a recorder temperature exceeds a reference value, the 8-fold-speed optical-disc recorder operates at the 4-fold speed. When surface vibration of the optical disc is small or when the recorder temperature drops below the reference value, the 8-fold-speed optical-disc recorder operates at the 8-fold speed.